1. Field of the Invention
The present invention concerns thruster systems for spacecraft. It is particularly, though not exclusively, concerned with thruster systems for carrying out requirements such as orbital manoeuvres, station keeping and attitude control.
2. Description of Related Art
Conventionally bipropellant thrusters are used which combine an oxidiser with a fuel for their propulsive effect. One commonly used oxidiser is dinitrogen tetroxide (N.sub.2 O.sub.4) whilst fuels used are hydrazine or hydrazine derivatives.
A problem arises in that thrusters of this type tend to produce more thrust than is necessary for attitude control requirements. Because of this spacecraft are often fitted with reaction or momentum wheels to provide fine control and to minimise the effect of relatively high thrust levels.